Why the sudden sprouting of chins at this late date? There's little data on which to venture a speculation at this time. However, the sudden sprouting of chins practically worldwide in those who are/will be the ancestors of 21st century humanity suggests one or more traumatic evolutionary events-- die offs resulting in such a small number of survivors that a small mutation like growing a chin can suddenly spread through a majority of the population afterwards. Indeed, there are indications of one or more such events between 400,000 BC and 69,000 BC.

Of course, there's also other possibilities. Such as one or more of the first major world wars fought around this time. Perhaps only a few thousand years earlier eurasian humanity had managed to domesticate the wolf. The use of wolves as hunting companions, camp guards, garbage disposals, and contingency food supplies could have spread across a large part of the human population by now.

The domesticated wolf would offer a terrific advantage to its master against anyone lacking such an animal. Something like a firearm will, later on in human history. And what happened in regards to firearms? They were first developed for purposes of war and defense.

Perhaps there were one or several 'wolf' wars. First, those 'armed' with wolves decimated those without. This taught all survivors the value of wolves, and domestication spread rapidly.

The presence of domesticated wolves could so empower humanity in general that it could allow for a population boom in the species (humanity), thereby leading to still more intensive and frequent conflicts and fighting. Note that the population boom would mainly occur among wolf owners (so even if no 'wars' take place, eventually the wolf owners would overwhelm the non-owners by sheer force of numbers).

The next major wolf war might have seen both sides so equipped, with the main deciding factors for a victor being attrition (victory through superior numbers, and/or better killing skills), and the quality of training and breeding (size, strength, speed, intelligence) in the wolves, and how well they and their masters worked together.

In all such wolf wars an unprotected human throat was decidedly inferior to a protected one. Thus, those with chins which could be dropped to protect the throat from wolf jaws survived more often that those without chins.

Of course, if this is how humanity acquired chins, that would signify a horrifically brutal and large scale extended conflict among most of humanity via their newly domesticated wolves. Due to a variety of factors, such conflicts likely would have had to rage for millennia to make chins appear as quickly as they did.

The actuality of thousands of years of wolf wars would also imply a larger eurasian population of humanity near the beginning of the wars than 20th century scientists will expect-- because otherwise population densities would be too low to allow such intensive conflict and casualties. Another implication however is an enormous death and injury toll from the fighting, equivalent perhaps to a third or even two thirds of humanity overall, by the time the wars are winding down (a rough stalemate is reached, or else population densities drop so low that it's difficult to find anyone to attack afterwards).

In one group of primitive peoples in the Ecuadorean Amazon studied by scientists, any given male possessed a 50% chance of being killed by another in the same vicinity. In general however the murder rate for males in primitive tribal societies appears to be around 30%.

The tendency to kill others seems to have evolved as a means for men to get ahead in tribal societies. The more they killed, the higher a status they gained in their society. The higher their status, the more wives they took, and the more children they likely fathered.

Fortunately, murder rates in modern civilization have diminished considerably compared to the tribal societies from which they sprang-- tribal cultures maintain rates about 50 times higher than that of modern developed nations, circa 2000 AD.

(Of course, societies in modern developed nations may simply have replaced physical murder with virtual murder-- as in actions of omission or commission which contribute to enemies losing their jobs, businesses, investments, savings, families, friends, allies, or other important elements of social stature. Keep in mind that symbolism and abstraction remain a hallmark of human development, and as such may still be progressing among us in a variety of ways. It would be interesting to see what the difference is between the physical murder rate in tribal societies and the virtual murder rate in modern ones-- if any difference exists at all.)

The measures here include the deaths in war as well as plain individual homicides.

-- Ask Dr. Universe
Survival of the meanest? Evolution hard-wires humans for violence, expert believes, May 9, 2000, The Seattle Times Company, AskDrUniverse@wsu.edu. Dr. W.S. Universe, Washington State University, Pullman, WA 99164-1040. http://www.wsu.edu/DrUniverse/ Ask Dr. Universe is a service of Washington State University